1. Field of the Invention
This invention relates to a shield machine used for making an enlarged tunnel by enlarging a portion of an existing tunnel and more particularly to a shield machine for removing back-filling material from a segment of a previously constructed, existing tunnel for facilitating a forward driving of a shield machine body.
2. Description of Background Art
In a process for enlarging a portion of an existing tunnel, a shield machine has been hithertofore known wherein its cutter head size is changed in the midst of the existing tunnel. In another process, after the excavation of an existing tunnel is completed, a shaft may be excavated from the ground surface thereto and an enlarged portion of the tunnel may be constructed by digging and utilizing this shaft.
However, these processes are low in efficiency and problematical in increasing the working time and cost.